Known in the art is a heterogeneous catalyst for the synthesis of aromatic monoisocyanates including m-bromo-, o- and p-chlorophenylisocyanate which contains 5 to 15% by weight of palladium supported on pumice promoted by salts of silver, manganese, cobalt, gold, nickel, iridium taken in an amount of from 5 to 20% by weight.
This catalyst is employed at a temperature within the range of from 100 to 240.degree. C. under a pressure of from 1 to 150 atm. Halosubstituted phenylisocyanates are produced using this catalyst within 1.2 to 3 hours with a yield of from 5 to 15%. The catalyst productivity is 0.5 to 1.5 g of the desired product per hour per one g of PdCl.sub.2 (cf. British Patent No. 1,205,521).
Also known in the art is a homogeneous catalyst comprising palladium chloride (0.5 to 5% by weight) in a mixture with acetonitrile. In the presence of this catalyst at a temperature of 200.degree. C. under a pressure of from 50 to 700 atm and within a period of from 4 to 8 hours of the reaction there are obtained p-chloro and 2,4,6-trichlorophenylisocyanates with a yield of from 24 to 35% at a conversion of the nitrocompound of from 44 to 87%. Productivity of this catalyst is 2 to 5 g of the desired product per hour and per g of PdCl.sub.2 (cf. U.S. Pat. No. 3,576,836). This prior art catalyst, however, has disadvantages including low activity and a long reaction time of up to 8 hours, as well as low productivity.
Also known in the art is a homogeneous-heterogeneous catalyst employed in the synthesis of aromatic monoisocyanates such as phenylisocyanate which contains 30 to 60% by weight of palladium chloride, and 40 to 70% by weight of vanadium pentoxide. In the presence of this catalyst, under a pressure of from 35 to 90 atm, a temperature of from 100.degree. to 220.degree. C., over a period of 4-5 hours, phenylisocyanate is obtained in a yield of from 82 to 92% at a conversion of nitrobenzene of from 90 to 100%. Selectivity is equal to 82-92%.
Disadvantages of this prior art catalyst include the necessity of its pre-treatment with carbon monoxide for the purpose of activation; a long reaction time of up to 5 hours and a low productivity of about 3 g of isocyanate per g of PdCl.sub.2 per hour.
It is an object of the present invention to overcome the above-mentioned disadvantages.
It is an object of the present invention to provide a catalyst for the synthesis of aromatic monoisocyanates which has high activity without any pre-treatment thereof.
It is another object of the present invention to provide a catalyst for the synthesis of aromatic monoisocyanates which would ensure high productivity of the synthesis.